In masts of storage and retrieval machines, the base connections of the mast may be subject to impact loads if the machine runs out of control or objects strike the mast. To provide a solid connection of the mast to the lower body of the storage and retrieval machine which will withstand impact loading, the bolts connecting the mast to the base are tightened to an preload tension. However, loss of a part of the tension over a period of time often occurs and the holding ability of the mast to base connections correspondingly decreases. A common cause of loss of preload tension is cyclic fatigue loading. Also, if scale, paint, burrs, or weld slag is present under the connecting bolt head or nut bearing surfaces, the projections of these materials will eventually flatten due to cold working during service. This will cause the grip length of the bolt to decrease slightly and thereby decrease the bolt preload tension.
Presently used bolted mast to base connections for storage and retrieval machines also are less capable of providing an adequate amount of preload tension, to withstand a vehicle crash having a force of one g. (that is, the force of gravity multiplied by one). With the advent of storage and retrieval machines running at higher speeds and carrying larger loads, the one g. vehicle crash specification for retaining mast connection integrity is now frequently required.